This invention relates to a television (hereafter referred to as "TV") receiver having a different aspect ratio which indicates a standard TV signal to a receiver having an oblong standard TV receiver and a high quality TV receiver.
In a high quality TV receiver which receives a signal from a high quality system (aspect ratio 16/9) and the present standard TV system (aspect ratio 4/3) having a different aspect ratio, the signal of the standard TV system is converted to the high quality TV system as a standard in the longitudinal length of the high quality TV CRT (cathode-ray tube) screen surface, thereby projecting the picture on the CRT surface in the state shown in FIG. 4, wherein the numeral 100 is a CRT screen surface having an aspect ratio larger than 4/3, such as in a high quality TV system, 101 is a picture surface area corresponding to the standard TV CRT, portions 102, 103 have no image signals from converted TV and areas where the images are not projected thereon respectively, and 102e, 103e are boundary line parts of the above area.
On the other hand, with the oblong standard TV receiver, although there is no need for the conversion of the above TV system signal, the image is projected on the screen surface in the state shown in FIG. 4. When the present standard TV signal is projected to the above high quality TV receiver or the oblong standard TV receiver, the following problems are caused beyond the boundary line portions 102e, 103e on both the right and left ends of the image surface 101.
As a conventional prior art for solving the above problems, patent publication No. Heisei 2 (1990) - 237282, "High Quality TV Receiver" is known.
In addition, as a patent wherein a velocity modulation circuit is used, the following is proposed.
The so-called use of a velocity modulation circuit, wherein a magnetic field in a horizontal direction is proportional to the amount of change (a differential amount) of a luminance signal each time during each horizontal scanning to increase the sharpness of the image, is piled on a horizontal deflection magnetic field whereby the horizontal scanning velocity is adapted to change to a speed higher or lower than the standard at the front or the rear portion where the luminance is subjected to change.
A conventional example wherein a velocity modulation circuit is used for a high quality TV receiver, is shown in FIG. 3.
In this case, the numeral 11 is an input terminal of a standard TV signal, 12 is a signal conversion circuit which converts the standard TV signal to the high quality TV signal, 12a is an output terminal of the luminance signal, 14 is a high quality TV receiver, 14a is an image signal treatment circuit, 14b is a CRT, 14c is a cathode, 14d is a grid electrode, 14e and 14f are a horizontal and a vertical deflection coil, respectively, 16 is a velocity modulation circuit, and 17 is a velocity modulation coil.
The output of the luminance signal generated at the above signal conversion circuit 12 or the image signal treatment circuit 14a is sent to the velocity modulation circuit 16, where the output is adapted to be sent to the velocity modulation coil 17 in a current output form which varies the horizontal scanning velocity to a velocity higher or lower than the standard one at the front or the rear portion of the luminance change. In this way, the image becomes sharper.
However, at the boundary lines 102e and 103e shown in FIG. 4, the velocity modulation circuit 16 causes a large change of the luminance signal, which causes ringings at the boundary line portions 102e and 103e of the CRT screen surface, and the picture consequently becomes glittered and ugly.
The object of this invention is to do away with the above problems and to provide a TV receiver having a velocity modulation circuit effect without such glittered and ugly images due to the ringing on the screen surface of the CRT indicator, even if the velocity modulation circuit is provided thereto, when the standard TV signal having a smaller aspect ratio is received by the high quality TV receiver or the oblong standard TV receiver.